The present invention relates to an adsorption bed and adsorption filtering system for removing airborne contaminants from enclosed interior rooms, particularly, rooms housing lithography processes.
Gas adsorption beds are used in many industries to remove airborne contaminants, such as organic bases, to protect people, the environment and often, a critical manufacturing process or the products that are manufactured. A specific example of an application for gas adsorption beds is the semiconductor industry where products are manufactured in an ultra-clean environment, commonly known in the industry as a xe2x80x9cclean roomxe2x80x9d. The manufacturing processes typically require the use of substances such as solvents to be used in the clean room environment. The use of these substances presents a problem because vapors that are present or are a byproduct from the process may contaminate the air and other processes in the room, such as lithography processes using chemically amplified photoresists, if not properly removed. In addition, environments may have gases that are naturally occurring in the ambient air, contaminants that cannot be removed by particulate filters. Typical previously recognized airborne contaminants include bases, such as ammonia, organic amines, and N-methyl-2-pyrrolidone.
To eliminate the airborne basic contaminants, contaminated air is often drawn through a granular adsorption bed assembly having a frame and an adsorption medium, such as activated carbon, retained within the frame. The adsorption medium adsorbs or chemically reacts with the gaseous contaminants from the airflow and allows clean air to be returned to the process and/or the clean room. The removal efficiency is critical in order to protect the processes and the products. The removal efficiency and capacity of the gaseous adsorption bed is dependent upon a number of factors, such as the air velocity through the adsorption bed, the depth of the bed, the type and amount of the adsorption medium being used and the activity level and rate of the adsorption medium. It is also important that for efficiency to be increased or maximized, the air leaking through voids between the tightly packed adsorption bed granules and the frame should be eliminated. Examples of granular adsorption beds include those taught is U.S. Pat. Nos. 5,290,245 (Osendorfet al.), 5,964,927 (Graham et al.) and 6,113,674 (Graham et al.).
Although the above identified adsorption beds, and other known beds, are used to remove bases, other airborne contaminants are also often present in the contaminated air. What is needed is an adsorption bed that can effectively remove both bases and other contaminants such as acids and other organic materials.
The invention is directed to an adsorption bed arrangement comprising a plurality of adsorption elements, a housing, and a gasket member between the housing and the adsorption elements. Each of the adsorption elements has a first adsorptive media and a second adsorptive media contained within a respective element. The first adsorptive media removes a first contaminant, such as acids, and the second adsorptive media removed a second contaminant, such as bases. Each of the adsorption elements is selectively openable to provide access to the adsorptive media. The elements are positioned within an interior of the housing, and the housing is selectively openable to provide access to the plurality of adsorption elements. In this manner, the adsorption elements can be accessed, opened, emptied of their existing media, and refilled with new, fresh adsorptive media.
Preferably, the housing has first and second opposite panels, and a side panel. The side panel is selectively removable to provide access to the adsorption elements. Preferably, the gasket member is situated in between to provide a seal between the side panel and the adsorption elements.
Preferably, each of the adsorption elements includes first and second opposite screens, an interior screen positioned between the first and second screens, and at least one open end. The first adsorptive media is removably packed between the first screen and the interior screen, and the second adsorptive media is removably paced between the interior screen and the second screen. In certain preferred arrangements, each adsorption element open end is covered with a removable cover member. Preferably, each of the cover members comprises a urethane pad.
In preferred arrangements, the adsorption bed assemblies are arranged in a vertical stack in an adsorption apparatus.
The invention is also directed to a method for changing filtering media in an adsorption apparatus. The method includes a step of removing an access panel from an adsorption bed housing to expose a cover member covering an end of an adsorption element. The cover member is removed from the end of the adsorption element to expose filtering media, such as first adsorptive media and second adsorptive media, within the element. The filtering media is then poured from the element. Preferably, after the step of pouring, new filtering media is added into the element. The cover member is then replaced over the end of the element, and the access panel is replaced on the adsorption bed housing.
In certain preferred methods, a first pre-filter is removed from the adsorption bed housing through a slot in the housing. After the step of removing a first pre-filter, a second, different and new pre-filter is inserted through the slot in housing.
These features and various other advantages that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.